The present invention relates to an optical light source arrangement and, in particular, relates to such a system having a redundant arrangement for the use of an optical communication system.
In an optical communication system using an optical fiber cable for a long line communication system, like an intercontinental communication line, the operational reliability of the system must be extremely high compared with that of a short communication line, since it takes a long time and much cost for repairing the fault when there is something wrong with the communication system.
In an optical communication system using an optical fiber cable and a plurality of optical repeaters, the most important element for improving the operational reliability of the system is an optical light source installed in each optical repeater for converting a repeated and/or amplified electrical signal to an optical signal which is to be transmitted to an optical fiber cable, since the operational reliability of that light source is relatively low compared with that of electrical components installed in an optical repeater.
Therefore, a redundant arrangement of an optical light source has been proposed for improving the operational reliability of an optical repeater.
FIG. 1 is the prior light source redundant arrangement, which is shown in the Japanese patent laid open publication No. 37023/80, in which S.sub.1, S.sub.2, S.sub.3 and S.sub.4 are light sources which provide the same wavelength of optical energy as one another, C.sub.1, C.sub.2 and C.sub.3 are optical couplers each of which is implemented by a rod lens or a simple connection of optical fibers. Each optical light source S.sub.1 through S.sub.4 is implemented by a light emitting diode (LED) or a laser diode, which is energized by an electrical circuit including an automatic power control (APC), a bias circuit, and a driving circuit (not shown). The symbol (f) shows an optical fiber.
One of the light sources S.sub.1 through S.sub.4 is selectively actuated, and when the light source is degraded, the operational light source is switched to another one.
However, the light source arrangement in FIG. 1 has the disadvantage that the insertion loss of an optical coupler is rather high. Generally, each optical coupler C.sub.1 through C.sub.3 has the insertion loss of approximate 3 dB, and since a pair of optical couplers C.sub.1 and C.sub.3, or C.sub.2 and C.sub.3 are inserted in series, the total insertion loss is 6 dB. That large insertion loss by optical couplers shortens the spacing between repeaters, and even when many light sources and many optical couplers are utilized, the operational reliability of the total communication system is not significantly improved.